The Kansas City Chiefs have a pretty simple formula for winning games—play great defense. For nine straight games, the Chiefs played great defense and they won all of those games.

Over the last three games, the Chiefs have struggled defensively. As a result, they have fallen to 9-3 and into second place in the AFC West. Either the Chiefs are going to have to find a new formula for success, or they are going to have to solve some of their defensive issues.

There are at least three theories for the Chiefs’ defensive struggles. One theory is simply that they played top-flight quarterbacks—Denver Broncos quarterback Peyton Manning twice and San Diego Chargers quarterback Philip Rivers.

Who/what is to blame for the defensive woes over the past three weeks?

The SecondaryThe Pass RushInjuriesNothing/Better CompetitionOtherSubmit Votevote to see results

Who/what is to blame for the defensive woes over the past three weeks?

The Secondary

44.5%

The Pass Rush

27.2%

Injuries

12.4%

Nothing/Better Competition

12.9%

Other

3.0%

Total votes: 986

Injuries could also be to blame because the Chiefs have been missing key contributors over the last two weeks. Defensive end Mike DeVito missed a game and outside linebacker Justin Houston missed a game after being knocked from the game a week earlier. Outside linebacker Tamba Hali also missed the better part of a game, but was able to return last week at something a lot less than 100 percent in the health department.

There is also the possibility that the Chiefs just aren’t playing or coaching as well on defense as they were earlier in the year. Opposing teams have now had time to study the scheme and the players in order to devise ways to beat them.

A Sick Secondary

One of the biggest problems for the Chiefs has been the play of the safeties. Eric Berry is the lone exception, but he is used in many different ways.

When the Chiefs do get good play from their safeties, the defense tends to be a lot better. This makes sense because cornerbacks Marcus Cooper, Brandon Flowers and Sean Smith have all had issues as well.

The one thing that is hard to blame is the scheme. Defensive coordinator Bob Sutton has done his best to make changes, but the Chiefs have been beat in a variety of different ways. When the Chiefs have had defensive success over the last three weeks, the scheme has had a lot to do with it.

Take a look at the alignment of safety Quintin Demps prior to the snap on Manning’s first interception last Sunday. Demps is right on the line of scrimmage, but he drops deep at the snap.

Game Rewind

Manning doesn’t see Demps sprinting over from the other side of the field and chooses to take a shot deep against Cooper against what he perceives to be no safety help. Cooper is in position to make a play, but Demps is able to haul in the juggling interception.

Game Rewind

This is the type of success the defense had for nine games, but the positive plays have been fewer and farther between in recent weeks. A big reason is that the quarterbacks the Chiefs have faced have been able to make adjustments and exploit even the slightest defensive weaknesses.

Prior to Manning throwing his first interception, the Chiefs were already getting gouged in the passing game. It didn’t take long for the Broncos to have success, even if the Chiefs were able to keep it close early. On two of the first three plays, Manning completed passes for 14 and 18 yards.

The 18-yard completion to wide receiver Wes Welker demonstrated how the Chiefs have struggled and why a quarterback like Manning was able to beat them. First, Manning gets amazing protection and the Chiefs opt to rush just four players.

Game Rewind

With extra defenders in coverage, the Chiefs should be able to cover every receiver and still have deep safety help. Instead, Manning anticipates Welker shaking free of Flowers and delivers an accurate pass. The safety—Kendrick Lewis—drops to his left and then is late to support even though there is no threat of a deep pass to that side.

In defense of Lewis, Manning does this to everyone and has for years. With such a clean pocket, the secondary doesn’t really have much of a chance.

On the 14-yard completion, Cooper was tossed aside as he tried to press wide receiver Demaryius Thomas at the line of scrimmage. Things didn’t get much better for Cooper as Manning picked on him for the entire game.

Cooper doesn’t have the foot quickness to stick with speedy receivers deep, so poor technique at the line of scrimmage has hurt him in both the short and deep passing games. It may be time to consider sitting the rookie down and having another player take his snaps for a while.

The Pressure Problem

When a defense can consistently get pressure, the entire defense plays better. Cornerbacks don’t have to cover for as long when there is pressure, so they are nearer to the receivers when passes arrive. Safeties can also drive on passes and not worry as much about them going over their heads.

When the pass rush isn’t getting to the quarterback, the secondary can’t be as aggressive or they will get beat—badly. At least that’s the case against quality quarterbacks.

Jamie Squire/Getty Images

It's really hard to sack Peyton Manning.

The Chiefs chose to take away the underneath passing game against Denver after getting burned by short crossing passes for two straight weeks. The results were much of the same even though the strategy was different, but the common denominator is a lack of pressure on the quarterback.

Manning was 5-for-6 for 212 yards, three touchdowns and one interception on passes traveling more than 20 yards in the air in Week 13, according to Pro Football Focus (subscription required). A week earlier, Rivers was 19-for-21 for 195 yards throwing short passes, and Manning was 21-for-28 for 204 yards on short passes in Week 11.

When a quarterback like Manning or Rivers can get rid of the ball so quickly, it’s very hard to get pressure on them. Manning was getting rid of the ball so quickly in Week 11 that the Chiefs didn’t even hit him.

The Chiefs were a little more productive getting pressure against the Chargers, but they had to blitz to do it. Berry had a sack and two hits and outside linebacker Frank Zombo had the only other hit, according to Pro Football Focus (subscription required), but that was it.

Pressure Problems?

Period

Sacks

Hits

Hurries

Total

Last 3 Average

0.3

2.0

12.0

14.3

Houston/Hali Contribution %

0.0%

0.0%

16.7%

14.0%

Last 9 Average

4.2

3.2

17.1

24.6

Houston/Hali Contribtion %

55.3%

51.7%

51.3%

52.0%

Percent Decrease

92.2%

37.9%

42.5%

41.9%

Houston/Hali Percent Decrease

100%

100%

67.40%

73.10%

ProFootballFocus.com

Sacks are down 92.2 percent over the last three games compared to the previous nine games for the Chiefs, while quarterback hits are down 37.9 percent and hurries are down 42.5 percent. The biggest decline in production has come from Hali and Houston.

The average sack rate of the 35 qualified quarterbacks, via Pro-Football-Reference.com, is 6.8 percent. Manning has just a 3.0 percent sack rate and Rivers is at 4.8 percent. That means Manning is roughly 56 percent less likely than the average quarterback to take a sack and Rivers is 29 percent less likely.

All things considered, the drop in pass-rush productivity was what we should’ve expected. The Chiefs faced a lot of bad quarterbacks through nine games, so their pass-rush statistics were a bit inflated.

Conclusion

Kansas City’s defense should rebound over the final four weeks against quarterbacks who take more sacks than Manning and Rivers, but don’t expect them to dominate like they did earlier in the season. As long as Houston is sidelined, the Chiefs will still be missing a big part of their pass rush.

At times, the Chiefs will be able to hide their flaws on defense, but it’s clear now it may not be against good quarterbacks. The Chiefs will have to find a new formula that includes their offense producing more points to win games.

The good news for the Chiefs is the offense looks like they are ready to carry a bigger load and the defense is still very talented. With some defensive tweaks over the final month, the Chiefs could still be a force in the AFC.